This invention relates to the field of optical imaging and more specifically to the field of medical imaging with interferometric detection.
Over the past decade there have been tremendous advances in biomedical imaging technology. For example, magnetic resonance imaging, X-ray computed tomography, ultrasound, and confocal microscopy are all in widespread research and clinical use, and have resulted in fundamental and dramatic improvements in health care. However, there are many situations where existing biomedical diagnostics are not adequate. This is particularly true where high resolution (xcx9c1 xcexcm) imaging is required. Resolution at this level often requires biopsy and histopathologic examination. While such examinations are among the most powerful medical diagnostic techniques, they are invasive and can be time consuming and costly. Furthermore, in many situations conventional excisional biopsy is not possible. Coronary artery disease, a leading cause of morbidity and mortality, is one important example of a disease where conventional diagnostic excisional biopsy can not be performed. There are many other examples where biopsy can not be performed or conventional imaging techniques lack the sensitivity and resolution for definitive diagnosis.
Moreover, for medical procedures such as balloon angioplasty, conventional techniques have not been able to provide high resolution imaging of the artery while a balloon is being inflated. Many other interventional procedures would greatly benefit from high resolution, in-vivo visualization technology. This technology would be useful for performing preoperative and post-operative diagnostics, to alert medical personnel to problems, or to avoid problems encountered during medical procedures.
The present invention seeks to overcome the problems associated with such conventional imaging techniques.
It is an object of this invention to provide an endoscopic imaging system that provides high resolution images and is useful during a medical procedure to enable medical personnel to view a procedure or actively help control the procedural process while it is occurring. In one embodiment the optical imaging system comprises an endoscopic unit and an interferometer for performing multi-dimensional scanning of a structure by utilizing an optical coherence tomography (OCT) technique. In one embodiment, the present invention uses OCT to perform high resolution imaging of structures. OCT measures the optical properties of a structure interferometrically using a short coherence length or frequency tunable light source.
In one embodiment the system includes an interferometer which includes a broadband optical radiation source; an optical radiation detector; a reference optical reflector; a first optical path leading to the reference optical reflector; and a second optical path including an endoscopic unit. The endoscopic unit, in one embodiment, includes an elongated housing defining a bore, within which is positioned a rotatable single mode optical fiber extending the length of the bore of the elongated housing. In an alternative embodiment, the endoscopic unit of the present invention includes a fixed fiber and rotatable optical beam directing elements at the distal end of the endoscopic unit. An optical beam directing system is coupled to the distal end of the rotatable single mode optical fiber and is positioned to transmit the optical radiation from the single mode optical fiber to the structure and to transmit reflected optical radiation from the structure to the single mode optical fiber. The optical beam directing system of the endoscopic unit typically includes a lens and a beam director located at the distal end of the single mode optical fiber and positioned to direct light from the single mode optical fiber to the structure. The beam director may include a prism, a lens or a mirror and may be driven from a motor external to the endoscope via a mechanical linkage, or may be driven from a micromotor.
The endoscopic unit also includes a transparent window typically formed at the distal end of the housing or around the circumference of the distal end thereof to permit the transmission of optical radiation to and from the structure. Additionally, an irrigation port may be formed in the housing for delivering fluid to the structure in question. The endoscopic unit can further include one or more inflatable balloons for performing procedures such as balloon angioplasty, for maintaining the opening in a vessel.
The interferometer of the system further includes a beam divider which divides the optical radiation from the optical radiation source along the first optical path to the reflector and along the second optical path to the structure being viewed. The optical radiation detector is positioned to receive reflected optical radiation from the reflector and reflected optical radiation from the structure and to generate a signal in response to the reflected optical radiation. A processor utilizes the signals from the detector to generate an image of the structure being viewed.
In one embodiment the reference optical reflector is typically coupled to a movable actuator to provide periodic movement to the reference mirror. In another embodiment the movable reference mirror is replaced with a static reference mirror and the broadband optical source replaced with a narrow bandwidth frequency tunable source, such as a semiconductor laser with tunable external gratings, a tunable solid state laser, or a dye laser. With such a source, optical radiation reflected from the structure being observed will arrive at the detector after the radiation reflected from the reference mirror is received at the detector. If the source is frequency modulated this delay will result in a beat frequency that is dependent on the difference between the distance from the detector to the reflection site within the structure, and the distance from the detector to the reference reflector. In still other embodiments of the present invention, the detector forming part of the imaging system includes a polarization diversity receiver, or alternatively a polarization analyzer. In still another embodiment the source consists of a broad band optical source, an interferometric detector using an optical spectrum analyzer wherein the Fourier transform of the spectrum is used to derive the reflectance profile of the sample.
It should be noted, that as used herein, the term endoscopic, applies to medical as well as non-medical imaging. One example of non-medical imaging in which the present invention may be used is as a replacement for a borescope to detect faults in cavities and bores in various industrial applications. For purposes of discussion only, the description to follow describes the present invention in terms of medical imaging, but the it is not the intent to limit the applications so described herein. Furthermore although the term endoscope is used, this invention directly relates to guidewires, catheters, and imaging with probes placed through trocars.